Only: chỉ … thôi

To say "only", put chỉ before the verb and thôi at the very end: Em chỉ uống cà phê đen thôi. I only drink black coffee. You can also use just one of them: Em chỉ uống cà phê đen and Em uống cà phê đen thôi mean the same. With both, it sounds most natural in speech.

Chỉ goes before the verb, not between the verb and the thing as English "only" sometimes does. It can also stand right before a number or amount: Chỉ hai trăm ngàn thôi. Only two hundred thousand. Thôi comes at the end, where only a little word like nha or ạ can follow it, and on its own it's everywhere in shops: Một cái thôi (just one), Dạ, em coi thôi (I'm just looking).

To say that only one person does something, start with chỉ có: Chỉ có anh Minh biết. Only Minh knows.

In Saigon, chỉ is also the word for "she" (folded from chị ấy), and as the person doing something it also comes right before a verb: Chỉ đi rồi. She's gone. The clue is what comes before it: after another person word (Em chỉ …), it means "only".

Mới before a number also means "only", in the sense of "only so few" or "only so young": Bé mới ba tuổi. That's a later pattern. Thôi! at the start of a sentence is different again: it means "that's enough" or "never mind".